Hydraulic actuators are used in a range of industries to control the position of a first part relative to a second part.
It is common for a hydraulic actuator to include a casing which defines a chamber having a gland at one end. A piston mounted at one end of a rod is slidably housed within the chamber, with the rod extending through the gland in the casing. Hydraulic fluid can be pumped into or out of the chamber on one side of the piston to drive the piston, thereby causing the actuator to extend or retract.
A centre seeking actuator is a known type of actuator which also includes a floating piston mounted within the chamber, the rod piston being slidably mounted within the floating piston and the rod extending through glands in both the floating piston and the casing. The floating piston divides the chamber into a control side arranged to receive hydraulic fluid and a side vented to atmosphere. Hydraulic fluid pumped into the control side moves the floating piston to reduce the size of the vented side. The hydraulic fluid also passes through control apertures in the piston or floating piston to enter the floating piston chamber and move the rod piston away from the vented side such that the actuator assumes an intermediate extension state which lies between fully extended and retracted states of the actuator.
The present inventors have identified that known hydraulic actuators can be improved in terms of their reliability and lifespan.